Endurance exercise training elicits physiological adaptations which increase the functional capacity of various organs. Older, physically well-trained "master" athletes tend to have a cardiovascular functional capacity (maximal oxygen consumption, VO2max) which more closely approximates that of much younger individuals than that of their sedentary peers. They also have higher levels of high density lipoprotein (HDL) cholesterol, lower percent body fat and their tissues are more insulin sensitive than that of age-matched sedentary controls. To examine the interrelationship of age and physical fitness to endocrine-metabolic function, a study was designed to examine serum lipid profiles, lipid metabolism, glucose metabolic rates and insulin sensitivity, and cardiovascular function in healthy lean older men (greater than 60 yrs), who are free of detectable coronary artery disease or metabolic dysfunction, and who have a wide range (25-50+ ml/kg.min) of VO2max. To evaluate the specific role of training on metabolic and cardiovascular function, highly trained individuals will be de-trained over a 3-month period; sedentary and less active subjects will be trained over a 6-9 month period. Thus, both groups will achieve a common level of VO2max. Endocrine-metabolic function studies include: 1) glucose tolerance, beta cell sensitivity, and insulin sensitivity using oral glucose challenge (OGTT) and euglycemic and hyperglycemic clamp techniques, 2) lipoprotein metabolism and lipoprotein lipase activity, and 3) sympathoadrenal responses to isometric exercise (handgrip), to cycle exercise, and to lower body negative pressure. To date baseline fasting glucose and lipid profiles have been obtained on 65 participants. Sixty-two subjects have had oral glucose tolerance tests, and 54 of the men qualified have undergone an initial treadmill screening test and maximal oxygen consumption (VO2max) test, 41 have undergone a second VO2max test and thallium scans, 6 have undergone hyperglycemic clamps with measurements of insulin receptor binding, 7 have undergone multigated cardiac blood pool scans and 8 have had HDL subfraction analysis with measurement of postheparin plasma lipoprotein lipase activity.